Full scale aerobatic pilots usually do wear full face helmets, and nearly every pylon pilot wears one. It is a requirement that pilots wear a helmet at Reno.

One of my friends was practicing his sequence in a Super Decathlon several years ago. His elevator cable failed while attempting to recover from a right hand spin. He was unable to push the door open, because it is on the right side of the plane. At 2000 Ft. AGL, he smashed the door open with his helmet and was able to exit the aircraft. Had he not been wearing a full face helmet, he probably would have died that day!
Doug